New Study Reaffirms HRT Link to Breast Cancer Rate Decline

The authors of the new study reviewed the medical histories of 7,386 women diagnosed with invasive breast cancer and treated at Kaiser Permanente Northwest between 1980 and 2006. The records were available through Kaiser Permanente's computerized database, which includes a tumor registry and clinical, pathology, radiology and pharmacy data systems.

From the early 1980s to the early 1990s, breast cancer rates rose 26 percent, then an additional 15 percent through 2001. From 2003 to 2006, rates dropped by 18 percent.

The 26 percent increase paralleled increases in the rates of mammograms as well as increases in the use of hormone therapy, especially combination therapy, the researchers said.

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The 15 percent increase -- from 1992 to 2002 -- echoed a continued rise in the use of hormone therapy, although mammogram rates remained stable from 1991 rates.

The drop in breast cancer rates starting in 2003 coincided with a 75 percent drop in hormone therapy rates, although mammography rates remained the same.

"When HRT went down, breast cancer rates went down and mammography rates remained the same," Glass said. "This was an important finding, because others had suggested maybe the drop in breast cancer rates was because mammograms had gone down, but it didn't happen in the Kaiser numbers. The only thing we can figure out is, it's probably related to HRT, that fluctuations in HRT are the most likely explanation for fluctuations in breast cancer rates."

The increase in breast cancer rates occurred primarily in women over the age of 45 who had estrogen receptor-positive breast cancer.

According to Glass, this study is the first to document all these different factors -- mammography, hormone therapy, breast cancer and estrogen-receptor status -- in one study.

But one expert found the study's conclusions lacking.

"This is an interesting look at the picture but really is not evidence-based medicine," said Dr. Lila Nachtigall, director of the women's wellness program at New York University Medical Center and professor of obstetrics and gynecology at New York University School of Medicine. The study did not correlate individual cases of breast cancer with hormone use, therefore issues of causality cannot be decided, she added.

"To try to prove causality is confusing to doctors and patients," she said. "I think it's a combination of things."

More information

For more on HRT, visit the U.S. National Library of Medicine.